A serious complication may be infected by a traditional encephalic surgery and even death may be caused. So years ago, a Swedish professor, Doctor Leksell, first presented a concept of “Stereotactic Radio surgery” (SRS), which is applying the theory of stereotaxic to use high-octane ray focusing irradiation and to destroy targeted organisms, thus to cure the sickness. Such kind of therapy which employ ray to treat an encephalic disease is named as stereotactic radiosurgery science, and it started a new century of no wound radiosurgery.
Ordinarily, a traditional radiotherapeutic instrument comprises of a ray source body, a switch and an end collimation body. FIG. 1 of the drawings shows an embodiment of the radiotherapeutic instrument of prior art, and FIG. 2 is the sectional view of the instrument in FIG. 1. As shown in FIGS. 1 and 2, the radiotherapeutic instrument comprises a ray source body 1 with a ray source cavity 4 and a pre-collimation hole 5 defined on, a switch 2 with a middle collimation hole 8 set on, an end collimation body 3 with an end collimation hole 9 defined on. The pre-collimation hole 5, middle collimation hole 8 and end collimation hole 9 can be connected to form a therapy path. The switch 2 usually is integrated as a whole, the middle collimation hole 8 will be moved into or out of alignment with the pre-collimation hole 5 of the ray resource body by the movement of the switch, therefore to open or close the therapy path. But with this configuration, the radial passageway will be entirely open or closed when switching on/off the ray resource, so the radiate amount can't be adjusted continuously and flexibly.